Currently, radio spectrum resources used in a cellular mobile communications network are limited to only some fixed frequency bands such as 900 MHz and 1800 MHz, and there are more high-band radio spectrum resources that are not used in the cellular mobile communications network. With an increase of mobile data traffic, how to effectively use a high-band radio spectrum resource in a cellular mobile communications network becomes an urgent problem to be resolved.
In an LTE (English: Long Term Evolution) system, two types of signal transmission modes are defined: an FDD (English: Frequency Division Duplex) mode and a TDD (English: Time Division Duplex) mode.
In the FDD mode, data is received and sent on two separate symmetric frequency channels, and a channel used for receiving data and a channel used for sending data are separated by using a guard band. This means that paired frequencies have to be used in the FDD, uplink data is distinguished from downlink data by using symmetric frequencies, and resource allocation is continuous in terms of time. In practical application, a disadvantage is as follows: Using the FDD mode for asymmetric service data reduces spectrum resource utilization.
In the TDD mode, a channel for receiving data and a channel for sending data are separated by means of time. Specifically, in a cellular communications network that uses the TDD mode, data of a receiver and data of a transmitter are carried by using channels that are at a same frequency and in different timeslots, and resource allocation is discontinuous in terms of time. In practical application, a disadvantage is as follows: In the TDD mode, a transmit channel and a receive channel that are at a same frequency are used. Consequently, intra-system interference and inter-system interference are caused. To avoid the inter-system interference, a relatively large guard band is reserved, and spectrum resource utilization is relatively low.
For a high-band radio spectrum resource, a bandwidth granularity (for example, 1 G or 2 G) in a subframe is far greater than a bandwidth granularity in a subframe in a current cellular communications network. If the foregoing TDD mode or the foregoing FDD mode is used, a problem of low spectrum resource utilization still exists.